1. Technical Field
The present disclosure generally relates to wellbore servicing fluids. More particularly, this disclosure relates to cement compositions and methods of making and using same.
2. Background
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. The main objectives of primary cementing operations include zonal isolation to prevent migration of fluids in the annulus, support for the casing or liner string, and protection of the casing string from corrosive formation fluids. Subsequent secondary cementing operations may also be performed to repair primary cementing problems or to treat conditions arising after the wellbore has been constructed.
Fluids used in servicing a wellbore may sometimes be lost to the subterranean formation while circulating the fluids in the wellbore. In particular, the fluids may enter the subterranean formation via depleted zones, zones of relatively low pressure, lost circulation zones having naturally occurring fractures, weak zones having fracture gradients exceeded by the hydrostatic pressure of the drilling fluid, and so forth. As a result, the service provided by such fluids is more difficult to achieve. For example, a drilling fluid may be lost to the formation, resulting in the circulation of the fluid in the wellbore being too low to allow for further drilling of the wellbore. Also, a secondary cement/sealant composition may be lost to the formation as it is being placed in the wellbore, thereby rendering the secondary operation ineffective in maintaining isolation of the formation.
Lost circulation treatments involving various plugging materials such as walnut hulls, mica, and cellophane have been used to prevent or lessen the loss of fluids from wellbores. The disadvantages of such treatments include the potential for damage to subterranean formations as a result of the inability to remove the plugging materials therefrom and the dislodgement of the plugging materials from highly permeable zones whereby fluid losses subsequently resume. One technique for preventing lost circulation problems has been to temporarily plug voids or permeable zones with Sorel cement compositions. Sorel cement compositions typically comprise magnesium oxide and a chloride or phosphate salt and water which together form for example magnesium oxychloride. Sorel cements can be removed with minimal damage to subterranean zones or formations by dissolution in acids. One challenge to the use of Sorel cements is that in order to control the rheology of the cement and achieve process-desired properties such as predictable thickening times and right angle set, the components of the cement are contacted in an obligatory sequence. This obligatory sequence introduces undesirable process limitations and impacts the cost and efficiency of wellbore servicing operations utilizing these types of cements. Accordingly, it would be desirable to develop Sorel cement compositions that can retain process-desired properties while having a flexible preparation sequence.